The purpose of the Specimen Assessment Core (SAC) is provision of a centralized resource to the individual projects for the optimal collection and appropriate storage of tissues and biological fluids, and for measurement of indices relevant to SIV and FIV infection, or models thereof, in all 4 mammalian species under study (human, rhesus macaque, feline, and mouse). The assay section of the SAC will assay the tissue samples, plasma, and culture material for cytokines, hormones, and provide drug monitoring of potential therapeutics. The activities of the histopathology section include performance of cat and monkey autopsies, processing and staining tissue from autopsies, providing materials for investigators, and isolating and analyzing nucleic acids. Within the context of a unified Center, the establishment of this SAC can readily be seen to have 2 immediate advantages. More uniform method approach across the 4 mammalian species of interest, and across the several labs and investigators, provides greater cross-relevance of data gathered in one species in its application to another species for further investigation. For the science in this center, it is crucial to have proper evaluation, handling, and archives of samples for the investigators' use. In this manner maximal information may be gained. The central SAC will minimize the need for individual investigators to "reinvent the wheel" in developing or choosing their specimen assessment assay methods when emerging testable hypotheses must be examined. With a research center, scientific quality and the cost-effectiveness of this Core approach is necessary.